National Ambient Air Quality Standards for Ozone: Final Response to Remand

On July 18, 1997, in accordance with sections 108 and 109 of the Clean Air Act (Act), EPA completed its review of the national ambient air quality standards (NAAQS) for ozone (O<INF>3</INF>) by promulgating revised primary and secondary standards (62 FR 38856; henceforth, "1997 final rule"). On May 14, 1999, the United States Court of Appeals for the District of Columbia Circuit ("D.C. Circuit") remanded the O<INF>3</INF> NAAQS to EPA to consider, among other things, any potential beneficial health effects of O<INF>3</INF> pollution in shielding the public from the "harmful effects of the sun's ultraviolet rays." 175 F.3d 1027 (D.C. Cir., 1999). Today's action provides EPA's final response to that aspect of the Court's remand. Based on its review of the air quality criteria and NAAQS for O<INF>3</INF> completed in 1997, its additional assessment of potential beneficial effects of tropospheric O<INF>3</INF>, and taking into account public comments, EPA has determined that information linking (a) changes in patterns of ground-level O<INF>3</INF> concentrations likely to occur as a result of programs implemented to attain the 1997 O<INF>3</INF> NAAQS to (b) changes in relevant patterns of exposures to ultraviolet (UV-B) radiation of concern to public health is too uncertain at this time to warrant any relaxation in the level of public health protection previously determined to be requisite to protect against demonstrated direct adverse respiratory effects of exposure to O<INF>3</INF> in the ambient air. Further, it is the Agency's view that associated changes in UV-B radiation exposures of concern, using plausible but highly uncertain assumptions about likely changes in patterns of ground-level ozone concentrations, would likely be very small from a public health perspective. As a result, the revised O<INF>3</INF> NAAQS will remain set at a level of 0.08 parts per million (ppm), with a form based on the 3-year average of the annual fourth-highest daily maximum 8-hour a